An observer based approach to force reflecting bilateral teleoperation

Bilateral teleoperation systems are an active area of research with possible applications in healthcare, remote surveillance and military, space and underwater operations, allowing human operators to manipulate remote systems and feel environment forces to achieve telepresence. The physical distance between the local and remote systems introduces delay to the exchanged signals between the two and cause instability in the bilateral teleoperation. With the advent of the internet, possible applications of bilateral teleoperation systems have proliferated, growing the interest and amount of research in the field. The delay compensation method for stable and force reflecting teleoperation proposed in this thesis is based on utilization of three different types of observers: A novel predictor observer that estimates the undelayed states of the remote system based on a nominal model, disturbance observers that eliminate internal and external disturbances and linearize the nonlinear dynamics of the two systems, and reaction torque observers that estimate the net external forces on the two systems. The controller for the remote system is placed at the local site, along with the predictor observer and the control input is sent to the remote system through the communication channel. Force reflection is achieved using a modified version of the 4-channel architecture where control input and position of the remote system and the environment force estimations are exchanged between the two systems. Performance of the proposed method is tested with Matlab/Simulink simulations and compared to two other methods in the literature. Real-time experiments under variable communication delay are also performed where the delay is both artificially created using Matlab/Simulink blocks and obtained via the internet by bouncing signals off a remote computer outside the Sabancı University campus. Both the simulations and experiments are executed on a pair of 1-DOF robot arms and a pair of 2-DOF pantograph robots. The results show that stable and force reflecting teleoperation is achieved with successful tracking performances of the remote system

Delay compensation for nonlinear teleoperators using predictor observers

This paper presents a delay compensation technique for nonlinear teleoperators by developing a predictor type sliding mode observer (SMO) that estimates future states of the slave operator. Predicted states are then used in control formulation. In the proposed scheme, disturbance observers (DOB) are also utilized to linearize nonlinear dynamics of the master and slave operators. It is shown that utilization of disturbance observers and predictor observer allow simple PD controllers to be used to provide stable position tracking for bilateral teleoperation. Proposed approach is verified with simulations where it is compared with two state-of-the-art methods. Successful experimental results with a bilateral teleoperation system consisting of a pair of pantograph robots also validates the proposed method

An observer based approach to force reflecting bilateral teleoperation

In this paper, the delay compensation problem is tackled in an observer framework by using three observers: A novel predictor observer (PROB), disturbance observers (DOB) and reaction torque observers (RTOB). The controller for the slave system is placed at the master side, along with the predictor observer and the control input is sent to the remote system through the communication channel. Transparency is achieved using a modified version of the 4-channel architecture. Performance of the proposed method is tested on a pair of 2-DOF pantograph robots with signals exchanged through the internet. The results show that stable and transparent teleoperation is achieved with successful tracking performances of the slave system